n - PATh :.: Process and Product Applied Thermodynamics research ...

General Introduction
animals. That is, in this case perfluoroalkanes act as the CO2-releasing and O2-carrying
vehicles.
I.4. Motivation
Despite the current interest in these fluorinated compounds, there are questions
relating their behaviour that are still unanswered, most of the times due to lack of
experimental data. For many of the applications discussed above, the importance of
density, vapour pressure and gas solubility data is clear. Also, from a fundamental point of
view, these data can provide information about bulk liquid structure, the organization of
the solvent around a solute and the interactions between them.
One of the first attempts to estimate the thermophysical properties of
perfluoroalkanes was reported by Lawson et al. (1978) who used a group-contribution
method specially developed for perfluoroalkanes, to calculate properties such as the
solubility parameter, the enthalpy of vaporization, vapour pressure and solubility of
oxygen at 298 K. The method can provide only a qualitative estimation of these properties
and only for one temperature. The use of common group-contribution methods to
thermophysical property estimation often cannot be applied because they do not have
information for the CF2 and CF3 groups or the information they have is not reliable, since it
is based on the rare experimental data reported for perfluoroalkanes.
Predictions of gas solubilities in perfluoroalkanes have been made using
Hildebrand’s solubility parameter δ (��Gjaldbaek,
1963 and Hildebrand, 1970). For two
fluids to be mutually soluble, they need to have similar δ �values. The δ values of
perfluoroalkanes are between 12 and 16 MPa 1/2 , as compared to 11.6 MPa 1/2 for oxygen,
12.3 MPa 1/2 for carbon dioxide, 14-18 MPa 1/2 for alkanes, and 47.9 for water.
Semiempirical approaches to gas solubilities were derived from the scaled particle theory.
These approaches express the free energy of solution as the sum of the free energies for
formation of cavities in the solvent and that of the interaction between solute and solvent
(Pierotti, 1976). Correlations also exist between O2 solubilities and the solvent’s surface
tension (Uhlig, 1937), the solubility parameter (Lee, 1970), solvent’s viscosity (Wesseler,
1977) and solvent’s compressibility (Serratrice, 1982) since these are all manifestations of
the solvent’s degree of cohesiveness.
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